The present invention relates to a novel polycarbonate and its use as a material for the production of moulded bodies and semi-finished products, especially for transparent applications, such as data stores or audio compact disks, sheets, multi-wall sheets, films, lamp housings, panes, especially panes for motor vehicles, headlamp lenses, but also for electrical applications or house building.
The preparation of aromatic polycarbonates by the melt transesterification process is known from the literature and is described, for example, in the Encyclopedia of Polymer Science, Vol. 10 (1969), Chemistry and Physics of Polycarbonates, Polymer, Reviews, H. Schnell, Vol. 9, John Wiley and Sons, Inc. (1964) and, starting from DE 1 031 512, in some patents.
In EP-B-360 578 there are described polycarbonates containing, end groups other than phenol. The polycarbonates obtained according to EP 360 578 have a markedly increased content of erroneous structures as compared with the polycarbonates synthesised in solution. As the result, such materials have disadvantages as regards melt stability, thermostability and constancy of colour.
The object was, therefore, to develop polycarbonates and a process for their objective preparation, having greater stability.
The object has been achieved by the synthesis of polycarboriates having a markedly reduced concentration of erroneous structures.
The present invention provides solvent-free, low-branching, thermoplastic, aromatic polycarbonates prepared by the transesterification process and having weight-average molecular weights Mw of from 2000 to 150,000, preferably from 4500 to 55,000, based on diphenols, chain terminators of formula (I) 
wherein R, Rxe2x80x2 and Rxe2x80x3 may each independently of the others represent H, optionally branched C1-C34-alkyl/cycloalkyl, C7-C34-alkaryl or C6-C34-aryl, and, optionally, branching agents, characterised in that structural elements of formula (II)
HOxe2x80x94Z(COOH)xe2x80x94OHxe2x80x83xe2x80x83(II)
have a value after total saponification and HPLC determination of less than 300 ppm, preferably from 0.03 ppm to 250 ppm, Z being as defined for formula (VI) and the acid group being in the or the position relative to a hydroxy group.
As compared with polycarbonates mis-structured in the usual manner, the polycarbonates according to the invention exhibit a substantially increased hydrolytic stability and an improved critical thickness, with otherwise comparable mechanical and thermal properties.
The polycarbonates according to the invention are prepared in the melt from dihydroxy compounds, dicarbonates, chain terminators and, optionally, branching agents.
Chain terminators within the context of the invention are those of formula (I) 
wherein R, Rxe2x80x2 and Rxe2x80x3 may each independently of the others represent H, optionally branched C1-C34-alkylcycloalkyl, C7-C34-alkaryl or C6-C34-aryl, for example
o-n-butylphenol, m-n-butylphenol, p-n-butylphenol,
o-isobutylphenol, m-isobutylphenol, p-isobutylphenol,
o-tert-butylphenol, m-tert-butylphenol, p-tert-butylphenol,
o-n-pentylphenol, m-n-pentylphenol, p-n-pentylphenol,
o-n-hexylphenol, m-n-hexylphenol, p-n-hexylphenol,
o-cyclohexylphenol, m-cyclohexylphenol, p-cyclohexylphenol,
o-phenylphenol, m-phenylphenol, p-phenylphenol,
o-isooctylphenol, m-isooctylphenol, p-isooctylphenol,
o-n-nonylphenol, m-n-nonylphenol, p-n-nonylphenol,
o-cumylphenol, m-cumylphenol, p-cumylphenol,
o-naphthylphenol, m-naphthylphenol, p-naphthylphenol,
2,5-di-tert-butylphenol, 2,4-di-tert-butylphenol, 3,5-di-tert-butylphenol,
2,5-dicumylphenol, 3,5-dicumylphenol,
4-phernoxyphenol, 2-phenoxyphenol, 3-phenoxyphenol,
3-pentadecylphenol, 2-pentadecylphenol, 4-pentadecylphenol,
2-phenylphenol, 3-phenylphenol, 4-phenylphenol,
tritylphenol, 3-triphenylmethylphenol, 2-triphenylmethylphenol,
also benzotriazole derivatives of the general formula (III) 
wherein Ra to Rf are as defined above for R, Rxe2x80x2and Rxe2x80x3, and chroman compounds such as 
preferably high-boiling phenols such as tritylphenol, cumylphenol, pentadecylphenol or chromans,
or also in the form of compounds that are capable of transesterification under the synthesis conditions, such as, for example, carbonates, oxalates; o-carboxylic acid esters or the like, with preference being given to the free phenols or the carbonic acid diesters of formula (IV) 
and formula (V) 
wherein R, Rxe2x80x2 and Rxe2x80x3 correspond to those of formula (I). Phenols or transesterification-active substances can be added to the synthesis individually or in the form of a mixture. Preferred mixtures are those with diphenyl carbonate. It is possible to add the phenol or the phenol-carrying compound at any time during the reaction, preferably at the beginning of the reaction, and the addition can be divided into several portions. The total amount of carbonic acid ester is from 100 to 130 mol %, preferably from 103 to 120 mol %, based on the dihydroxy compound.
For the preparation of polycarbonates by the process according to the invention it is possible to use a chain terminator or a mixture of several chain terminators, so that there may be present as an end group in the polycarbonate according to the invention phenol but also phenol together with other chain terminators. From 0.4 to 17 mol %, particularly preferably from 1.3 to 8.6 mol % (based on the dihydroxy compound), of chain terminator are preferably added. The addition may take place either before the reaction or wholly or partially during the reaction.
Dihydroxy compounds within the context of the invention are those of formula (VI)
HOxe2x80x94Zxe2x80x94OHxe2x80x83xe2x80x83(VI)
in which Z is an aromatic radical having from 6 to 30 carbon atoms which may contain one or more aromatic nuclei, may be substituted and may contain aliphatic or cycloaliphatic radicals or alkylaryls or hetero atoms as bridge members.
Examples of dihydroxy compounds of formula (VI) are
hydroquinone,
resorcinol,
dihydroxydiphenyls,
bis-(hydroxyphenyl)-alkanes,
bis-(hydroxyphenyl)-cycloalkanes,
bis-(hydroxyphenyl) sulfides,
bis-(hydroxyphenyl) ethers,
bis-(hydroxyphenyl) ketones,
bis-(hydroxyphenyl)-sulfones,
bis-(hydroxyphenyl) sulfoxides, xcex1xcex1xe2x80x2-bis-(hydroxyphenyl)-diisopropylbenzenes and their nuclear-alkylated and nuclear-hydrogenated compounds.
These and other suitable diphenols are described, for example, in U.S. Pat. Nos. 3,028,365, 3,148,172, 3,275,601, 2,991,273, 3,271,367, 3,062,781, 2,970,131 and 2,999,846, in German Offenlegungsschrift 1,570,703, 2,063,050, 2,063,052, 2,211 0956, in French Patent Specification 1 561 518 and in the monograph xe2x80x9cH. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964xe2x80x9d.
Examples of preferred diphenols are:
4,4xe2x80x2-dihydroxydiphenyl,
2,2-bis-(4-hydroxyphenyl)propane,
2,4-bis-(4-hydroxyphenyl)-2-methylbutane,
1,1-bis4-hydroxyphenyl)cyclohexane,
1,1-bis-(4-hydroxyphenyl)4-methyicyclohexane,
xcex1,xcex1xe2x80x2-bis-(4-hydroxyphenyl)-p-diisopropylbenzene,
xcex1,xcex1-bis-(4-hydroxyphenyl)-m-diisopropylbenzene,
bis-(4-hydroxyphenyl)sulfone,
bis-(4-hydroxyphenyl)methane,
1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,
2,2-bis-(2,6dimethyl-4-hydroxyphenyl)propane,
2,2-bis-(4-hydroxyphenyl)hexafluoropropane,
1,1-(4-hydroxyphenyl)- 1-phenylethane,
bis-(4-hydroxyphenyl)diphenylmethane,
dihydroxydiphenyl ether,
4,4xe2x80x2-thiobisphenol,
1,1-bis-(4-hydroxyphenyl)-1-(1-naphthyl)ethane,
1,1-bis-(4-hydroxyphenyl)-1-(2-naphthyl)ethane,
2,3-dihydroxy-3-(4-hydroxyphenyl)-1,1,3-trimethyl-1H-inden-5-ol,
2,3-dihydroxy-1-(4-hydroxyphenyl)-1,3,3-trimethyl-1-H-inden-5-ol, 2,2xe2x80x23,3xe2x80x2-tetrahydro-3,3,3xe2x80x23xe2x80x2-tetramethyl-1,1xe2x80x2spirobi[1H-indene]-5,5xe2x80x2s-diol.
Special-preference is given to resorcinol,
1,1-bis-(4-hydroxyphenyl)-1-(1-naphthyl)ethane,
1,1-bis-(4-hydroxyphenyl)-1-(2-naphthyl)ethane,
2,2-bis-(4-hydroxyphenyl)propane, xcex1,xcex1xe2x80x2-bis-(4-hydroxyphenyl)-p-diisopropylbenzene,
xcex1,xcex1xe2x80x2-bis-(4-hydroxyphenyl)-m-diisopropylbenzene,
1,1-bis-(4-hydroxyphenyl)cyclohexane,
1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,
bis-(4-hydroxyphenyl)diphenylmethane,
4,4xe2x80x2-dihydroxydiphenyl.
It is possible to use both one diphenol of formula (VI), with formation of homo-polycarbonates, and several diphenols of formula (VI), with formation of copolycarbonates.
Low-branching within the context of the invention means that the content of formula (II) in the polycarbonate has a value after total saponification and HPLC determination of less than 300 ppm, preferably from 0.03 ppm to 250 ppm.
The polycarbonates can be branched in a deliberate and controlled manner by the use of small amounts of from 0.02 to 3.6 mol % (based on the dihydroxy compound) of branching agents. Suitable branching agents are the compounds which are suitable for the preparation of polycarbonates and contain three or more functional groups, preferably those containing three or more than three phenolic OH groups.
Examples of suitable branching agents are phloroglucinol,
4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)heptane,
1,3,5-tri-(4hydroxyphenyl)benzene,
1,1,1-tri-(4-hydroxyphenyl)ethane,
tri-(4-hydroxyphenyl)phenylmethane,
2,2-bis-[4,4-bis(4-hydroxyphenyl)cyclohexyl]propane,
2,4-bis-(4-hydroxyphenyl-isopropyl)phenol,
2,6-bis-(2-hydroxy-5-methylbenzyl)-4-methylphenol,
2-(4-hydroxyphenyl)-2-(2,4dihydroxyphenyl)propane,
hexa-[4(4-hydroxyphenyl-isopropyl)phenyl]orthoterephthalic acid ester,
tetra-(4-hydroxyphenyl)methane,
tetra-[4-(4-hydroxyphenyl-isopropyl)phenoxy]methane,
4-bis-[4xe2x80x2,4xe2x80x3-dihydroxytriphenyl)methyl]benzene,
xcex1,xcex1xe2x80x2,xcex1xe2x80x3tris-(4-hydroxyphenyl)-1,3,4-triisopropenylbenzene,
isatinbiscresol,
pentaerythritol,
2,4-dihydroxybenzoic acid,
trimesic acid,
cyanuric acid.
1,1,1-tri-(4-hydroxyphenyl)ethane and isatinbiscresol are particularly preferred.
As catalyst for the preparation of the polycarbonates according to the invention there may be used phosphonium salts, optionally in combination with other suitable catalysts which do not lead to erroneous structures such as formula (II), such as, for example, other onium compounds.
Phosphonium salts within the context of the invention are those of formula (VII) 
wherein R1-4 may be the same or different C1-C18-alkyls, C6-C14-aryls, C7-C12-aralkyls or C5-C6-cycloalkyls, preferably methyl or C6-C14-aryls, particularly preferably methyl or phenyl, and Xxe2x88x92 may be an anion, such as a sulfate, hydrogen sulfate, hydrogen carbonate, carbonate, acetate, boranate, hydrogen phosphates, a halide, preferably a fluoride, chloride or bromide, or an alcoholate of the formula OR wherein R may be C6-C14-aryl or C7-C12-aralkyl, preferably phenyl.
Preferred catalysts are
tetraphenylphosphonium fluoride,
tetraphenylphosphonium tetraphenylboranate,
particularly preferably tetraphenylphosphonium phenolate.
The preparation of the polycarbonates according to the invention is carried out, for example, as follows: in the first step, the diphenols, the carbonic acid diesters, the catalyst and, optionally, the alkylphenols and branching agents are melted at temperatures of from 75xc2x0 C. to 225xc2x0 C., preferably from 105xc2x0 C. to 235xc2x0 C., particularly preferably from 120xc2x0 C. to 190xc2x0 C., under normal pressure within a period of from 0.1 to 5 hours, preferably from 0.25 to 3 hours. Then the oligocarbonate is prepared by applying a vacuum and raising the temperature by removing the monophenol by distillation. In the last step, the polycarbonate is prepared in the polycondensation by raising the temperature further to from 240xc2x0 C. to 325xc2x0 C. and at a pressure of  less than 2 mbar.
In the preparation of polycarbonates by the melt transesterification process, the reaction of the bisphenol and the carbonic acid diester may be carried out continuously or discontinuously, for example, in stirrer vessels, thin-layer evaporators, falling film evaporators, stirrer vessel cascades, extruders, kneaders, simple disk reactors and high-viscosity disk reactors.
solation of the polycarbonates according to the invention is likewise carried out in a known manner, for example by removing, spinning and granulating.
The polycarbonates according to the invention can have weight-average molecular weights Mw of approximately from 2000 to 150,000, preferably approximately from 4500 to 55,000, Mw being determined via the relative solution viscosity in dichloromethane or in mixtures of equal amounts by weight of phenol/o-dichlorobenzene, calibration being by means of light scattering.
The polycarbonates according to the invention have the usual OH end group contents known from the literature, which can be determined by photometry using titanium tetrachloride.
The polycarbonates according to the invention can be processed thermoplastically in the usual manner at temperatures of from 260xc2x0 C. to 320xc2x0 C. Moulded bodies and films of any kind can be produced in a known manner by injection moulding or by means of extrusion.
The polycarbonates according to the invention are readily soluble in solvents such as chlorinated hydrocarbons, for example methylene chloride, and can therefore be processed, for example, in a known manner to cast films.
Accordingly, the invention also provides a process for the preparation of the low-branching polycarbonates according to the invention, characterised in that there are used as catalyst phosphonium salts of formula (VDI) in concentrations of from 10xe2x88x922 mol to 10xe2x88x926 mol, based on 1 mol of diphenol, optionally in combination with other suitable catalysts which do not lead to erroneous structures such as formula (II), such as, for example, other onium compounds.
In order to improve the properties, auxiliary substances and reinforcing agents can be added to the polycarbonates according to the invention. The following, inter alia, are to be taken into consideration as such: stabilisers, flow auxiliaries, mould-release agents, fireproofing agents, pigments, finely divided minerals, fibrous materials, for example alkyl and aryl phosphites, phosphates and phosphanes, low-molecular-weight carboxylic acid esters, halogen compounds, salts, chalk, quartz powder, glass and carbon fibres, pigments and combinations thereof.
Other polymers, for example polyolefins, polyurethanes, polyesters and polystyrene, may also be added to the polycarbonates according to the invention.
Excellent properties are achieved with that material even in moulded bodies.
Accordingly, the present invention relates also to the use of the low-branching, solvent-free, aromatic polycarbonates according to the inventionfor the production of moulded bodies and semi-finished products, especially for transparent applications, such as data stores or audio compact disks, sheets, multi-wall sheets, films, lamp housings, panes, especially panes for motor vehicles, headlamp lenses, but also for electrical applications or house building.